The new species, Pelagornis sandersi, had an estimated wingspan of 20 to 24 feet (6.1 to 7.3 meters) when its feathers are included. This is up to more than twice as big as that of the royal albatross, the largest living flying bird, which has a wingspan of about 11.4 feet (3.5 meters). [See Images of Giant Flying Species & Other Huge Birds]

"It's a really remarkable species,"study author Daniel Ksepka, a paleontologist and curator of science at the Bruce Museum in Greenwich, Connecticut, told LiveScience. "It really pushes the limits of how big we think flying birds can get. Getting a chance to add something like this to the avian evolutionary tree is really exciting."

Until now, the biggest known flying bird was the extinct Argentavis magnificens, a condorlike titan from Argentina.

"It's disputed how large Argentavis' wingspan was — we only have one wing bone for it," Ksepka said. "We think the wingspan of Argentavis' skeleton was a bit under 4 meters (13.1 feet), while the skeletal wingspan of P. sandersi was about 5.2 meters (17 feet). Now both of their wingspans would be longer once feathers are taken into account, but P. sandersi would still probably be larger than Argentavis."

The fossil was first unearthed in 1983 near Charleston, South Carolina, when construction workers began excavations for a new terminal at the Charleston International Airport. It was named Pelagornissandersi in honor of retired Charleston Museum curator Albert Sanders, who led the fossil's excavation.

Giant bird, giant dig

The specimen was so large that it had to be dug out with a backhoe. "The upper wing bone alone was longer than my arm," Ksepka said in a statement.

The specimen, which consisted of multiple wing and leg bones and a complete skull, was very well-preserved, a rarity because of the paper-thin nature of the bones in these birds. Its beak possessed bizarre toothlike spikes that lined the upper and lower jaws, revealing the bird was a previously unknown species of pelagornithid, an extinct group of giant seabirds known for these "pseudo-teeth."

"These pseudo-teeth were not made with enamel like true teeth are, but were projections of bone from the jaw," Ksepka said. "They are very conical and pointed, which suggests they were used for piercing prey. The most likely source of food for these birds were fish and squid near the surface of the water."

This pelagornithid lived 25 million to 28 million years ago. "During this time, global temperatures were substantially warmer than they are today, and sea levels were higher, since there was less ice at the poles," Ksepka said. "Charleston, where this fossil was found, is a lovely city today, but back then it was completely underwater."

Pelagornithids lived all over the globe for tens of millions of years, but vanished just 3 million years ago, and paleontologists remain uncertain as to why.

The paper-thin hollow bones, stumpy legs and giant wings of P. sandersi hinted the bird flew. However, its size exceeded what some models suggest were the theoretical limits for flying birds.

Could P. sandersi fly?

To find out how P. sandersi could take off and stay aloft despite its giant size, Ksepka fed data about the bird's mass, wingspan and wing shape into a computer program designed to predict flight performance. The researchers estimated the bird weighed from 48.2 to 88.4 lbs. (21.9 to 40.1 kilograms).

The model suggested the bird was an incredibly efficient glider, whose long, slender wings helped it stay aloft despite its enormous size. It was probably too big to take off simply by flapping its wings and launching itself into the air from a standstill — instead, like Argentavis, P. sandersi may have gotten off the ground by running downhill into a headwind or taking advantage of air gusts to get aloft, much like a hang glider.

"Pelagornis sandersi could have traveled for extreme distances while crossing ocean waters in search of prey," Ksepka said in a statement. "That's important in the ocean, where food is patchy."

By riding on air currents that rise up from the ocean's surface, P. sandersi was able to soar over the ocean without flapping its wings. Once P. sandersi reached adulthood, it may have been able "to live flying over the ocean for most of the year, coming back to land only to nest, flying for thousands of kilometers over the course of the year," Ksepka said. "It probably landed on islands or remote areas where they could avoid predators when they nested."

Unusually, "it's quite likely it had to molt all its flight feathers at the same time," Ksepka said. Flight feathers need to get molted once they no longer become flightworthy, and the bigger they get, the longer they take to grow back. To deal with this problem, they may have done what birds known as grebes do nowadays, and shed all their flight feathers simultaneously — "at the size they reached, it's very difficult to do anything else," Ksepka said.

Future research can analyze how these birds took off and landed, and how maneuverable they were in the air, Ksepka said. He detailed his findings online today (July 7) in the journal Proceedings of the National Academy of Sciences.